There are many acute and chronic diseases/disorders that are inflammatory in their nature including but not limited to rheumatoid diseases e.g. rheumatoid arthritis, osteoarthritis, diseases of the visceral system e.g. inflammatory bowel syndrome, autoimmune diseases, e.g. lupus erythematodes, lung diseases like asthma and COPD. Current treatment with non-steroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase (COX)-2 inhibitors are efficacious, but show a prevalence for gastrointestinal and cardiovascular side effects. There is a high need for new treatment options showing equivalent efficacy with an improved side effect profile.
mPGES inhibitors may show such an improved side effect profile because they block the generation of PGE2 in a more specific manner as described below.
NSAIDs and COX-2 inhibitors reduce inflammation and pain through inhibition of one or both isoformes of COX enzymes. The cyclooxygenase (COX) enzyme exists in two forms, one that is constitutively expressed in many cells and tissues (COX-1), and one that in most cells and tissues is induced by pro-inflammatory stimuli, such as cytokines, during an inflammatory response (COX-2). COXs metabolise arachidonic acid to the unstable intermediate prostaglandin H2 (PGH2). PGH2 is further metabolized to other prostaglandins including PGE2, PGF2α, PGD2, prostacyclin and thromboxane A2. These arachidonic acid metabolites are known to have pronounced physiological and pathophysiological activity including pro-inflammatory effects. PGE2 in particular is known to be a strong pro-inflammatory mediator, and is also known to induce fever, inflammation and pain. Consequently, numerous drugs were developed with a view to inhibiting the formation of PGE2, including “NSAIDs” (non-steroidal antiinflammatory drugs) and “coxibs” (selective COX-2 inhibitors). These drugs act predominantly by inhibition of COX-1 and/or COX-2, thereby reducing the formation of PGE2. However, the inhibition of COXs has the disadvantage that it results in the reduction of the formation of all metabolites downstream of PGH2, some of which are known to have beneficial properties. In view of this, drugs which act by inhibition of COXs are therefore known/suspected to cause adverse biological effects.
For example, the non-selective inhibition of COXs by NSAIDs may give rise to gastrointestinal side-effects and affect platelet and renal function. Even the selective inhibition of COX-2 by coxibs, whilst reducing such gastrointestinal side-effects, is believed to give rise to cardiovascular problems.
An alternative treatment of inflammatory diseases that does not give rise to the above-mentioned side effects would thus be of real benefit in the clinic. In particular, a drug that preferably inhibits the transformation of PGH2 to the pro-inflammatory mediator PGE2 selectively might be expected to reduce the inflammatory response in the absence of a corresponding reduction of the formation of other, beneficial arachidonic acid metabolites. Such inhibition would accordingly be expected to alleviate the undesirable side-effects mentioned above.
PGH2 may be transformed to PGE2 by prostaglandin E synthases (PGES). Two microsomal prostaglandin E synthases (mPGES-1 and mPGES-2), and one cytosolic prostaglandin E synthase (cPGES) have been described. mPGES-1 is proposed to be closely linked to COX-2 and both enzyme's are upregulated during e.g. inflammation. Thus agents that are capable of inhibiting the action of mPGES-1 and thereby reducing the formation of PGE2 are likely to be of benefit for the treatment of inflammation and more general acute and chronic pain conditions